exposure ended. The water parameters remained constant, although minor changes in
dissolved oxygen were observed (6.26 F 0.20 to 5.99 F 0.20 mg l 1
).
The long-term treatment at 4 mg l 1 (Fig. 4) produced similar results as the short-term
treatment. After 7 h of exposure, the number of parasites on the skin and gills of the fish
were reduced significantly (66% and 84%, with P= 0.021 and P= 0.001, respectively) in
comparison to the controls. The comparison between controls before and after the
treatments did not show significant differences for skin and gills ( P = 0.937 and
P= 0.937, respectively). No mortality, changes in behavior, or lesions were observed
during exposure to formalin. Only minor changes in dissolved oxygen (7.59 F 0.20 to
6.68 F 0.20 mg l 1
) were registered.